He said during his short life, Jamie had been subjected to violence on at least two and probably three occasions.

The judge said Parker would serve her time in a young offenders institution and Kightley would be sent to prison.

A murder charge against the couple was dropped during the trial.

The prosecution said Jamie had been assaulted about two weeks before he died and again hours before his death, but that both parents had "hidden behind a wall of silence" regarding who was responsible.

Medical evidence showed Jamie suffered injuries consistent with being grabbed around the middle and shaken, the jury heard.

Jamie Kightley lived with his parents at London Road, Northampton

Kightley and Parker agreed they had been drinking and smoking cannabis the night before Jamie's death but denied doing anything to harm their son.

When asked about bruises on his body, Parker claimed she had not seen them until Jamie was in hospital.

Judge Baker said the baby had been shaken with sufficient violence to cause him to suffer bleeding to the eyes and brain damage leading to his death as a result of respiratory and cardiac arrest.

'Substantial culpability'

He told the couple that "the episodes of violence would not only have caused pain and upset to Jamie but, more significantly, would have caused visible bruising to his body, which should at the very least have asked you to seek prompt medical attention".

"Not only did each of you fail to do so during the days leading up to his death, but I am quite satisfied that in order to cover up for this failure, you concocted a story.

"You maliciously suggested that you had previously shown bruising to a local GP who had dismissed it as unimportant."

He said the couple had deceived the police in interviews by appearing to want to help them.

"As a result of the stance which both of you took in the course of your interviews and during your evidence at trial, the identity of the perpetrator of these episodes of violence may never be known.

"You are to be punished for allowing his death to occur."

He added that the couple were "both young and both of you showed elements of care to your son during his short life", but was "satisfied that the level of culpability is substantial and the only sentence which can be justified for this offence is one of immediate custody".